Cardiac progenitor cells (CPCs) express an impressive complement of G-protein coupled receptors (GPCRs) distinct from those found on adult cardiomyocytes. This proposal tests the hypothesis that the expression of GPCRs and availability of their ligands at sites of injury can either enable or impair the proliferation, survival and differentiation of endogenous CPCs. We propose three aims in which we use CPCs isolated from WT and genetically engineered mouse hearts to examine GPCR regulated pathways that contribute to these responses and extend our findings to an in vivo myocardial infarct model. In Aim # 1 we use mRNA arrays, qPCR and protein expression assays to define resident GPCRs on cultured CPCs and determine if they are dynamically regulated by ischemic stress, ER stress, or differentiation. Further studies define the GPCRs that are most efficacious for eliciting CPC proliferation, survival, migration and differentiation and the specific G-proteins and effectors they utilize. In Aim #2 we test the hypothesis that RhoA signaling, and its regulation by SIP and other GPCRs can enhance the reparative properties of CPCs. Proposed studies use CPCs from genetically engineered RhoA and SIP receptor knockout mice to determine the SIP receptor subtypes and requirement for RhoA signaling in agonist stimulated CPC responses. The role of RhoA in activating and utilizing the downstream transcriptional co-activators MRTF-A and YAP is also examined. In vivo studies in SIP receptor and RhoA KO mice examine the regenerative capacity of resident CPCs following myocardial infarction (Ml). Aim #3 tests the hypothesis that changes in the complement of adrenergic (AdR) and Angll receptor (ATR) subtypes alter the proliferation and survival of CPCs and can induce mitochondrial damage and cell death through oxidative stress.We compare CPCs in which the complement of Pi vs. P2 and ATi vs. AT2 subtypes are altered and examine effects of ATR blockers and p-AdR blockers on proliferation and survival of CPCs. A final focus is on the possible salutary role of apAdR on CPCs in responses to sympathetic adrenergic stimulation and Ml. Our overall objective is to demonstrate that specific GPCRs and their signaling pathways can be used to maintain and enhance CPC function, with the long term goal of using these highly accessible drug targets as sites of intervention to promote myocardial healing. RELEVANCE (See instructions): Cardiomyocytes in the heart die when deprived of oxygen and as a consequence the heart becomes weak. Stem cells in the heart, if appropriately stimulated, could form new cardiomyocytes and prevent heart failure. We believe that specific G-protein coupled receptors on these cardiac progenitor cells may enhance this process and that drugs that regulate these receptors could be developed to heal the heart.